1. Field of the Invention
The present invention relates to improved methods for extraction of carotenoids from carotenoid-containing plant material. More particularly, the invention relates to methods for extracting carotenoids from plant material using ethyl lactate. The invention is also directed to products obtained by the methods.
2. Description of the Art
Carotenoids are natural pigments that occur in bacteria, plants, fungi, and animals. Carotenoids comprise a class of hydrocarbons (carotenes) and their oxygenated derivatives (xanthophylls). Most carotenoids are 40 carbon isoprenoid compounds called tetraterpenes. Carotenoids having fewer than 40 carbons can result from loss of carbons within the chain (norcarotenoids) or loss of carbons from the end of the molecule (apocarotenoids). Longer carotenoids, homocarotenoids (C45-C50), are found in some bacterial species. The alternating double bonds along the backbone of carotenoid molecules form a polyene chain, which imparts unique qualities to this group of compounds. This alternation of single and double bonds also allows a number of geometrical isomers to exist for each carotenoid. Carotenoids exist in both trans- and cis-isomeric forms of which the former can be converted to the latter by exposure to light, heat, or chemical reaction.
Carotenoids cannot be synthesized by humans, hence, must be obtained from dietary sources. For humans the most important sources for carotenoids are plants. These are primarily highly pigmented red, orange, and yellow fruits and vegetables. Exemplary carotenoids found in fruits and vegetables are lycopene, β-carotene, lutein, zeaxanthin, lutein plus zeaxanthin, β-cryptoxanthin, and α-carotene. Lycopene is typically the carotenoid consumed in greatest amounts in Western diets. Per capita intakes in Europe and North America average from 1.6 to more than 18 mg lycopene per day. More than 85% of the lycopene in North American diets comes from tomato products, which also contain significant amounts of other carotenoids (α- and β-carotene and lutein/zeaxanthin).
More than 20 pigments in the carotenoid class have been identified and quantified in tomatoes with lycopene being the principal carotenoid. Typically lycopene amounts to 85-90% by weight of the carotenoids in tomatoes. Concentrations of lycopene in common tomatoes ranges from 30 to 100 ppm, on the average at 50 ppm, fresh weight basis. Low amounts of other carotenoids such as α-carotene, β-carotene, γ-carotene, ε-carotene, phytoene, phytofluene, neurosporene, and lutein are also present in tomatoes. Lycopene provides the richness and bright red color to the tomato, making it commercially important as a natural pigment. Processed foods are frequently fortified with carotenoids such as lycopene to increase nutritive value and/or enhance attractiveness.
Carotenoids are important factors in human health. The essential role of β-carotene as an important dietary source of vitamin A has been known for many years. More recently, protective effects of carotenoids against serious disorders such as cancer, heart disease, and degenerative eye disease have been recognized.
Carotenoids act as antioxidants and/or singlet oxygen quenchers or as free radical scavengers. With 11 conjugated double bonds and no cyclic groups, lycopene is the most potent biological antioxidant. Of the many health benefits attributed to the consumption of carotenoids, these provide the greatest clinical depth.                Lycopene is an important antioxidant and free radical scavenger.        Free radicals can cause damage both to the structure and to the function of cell membranes, DNA, and proteins. This damage has been linked to the onset of many degenerative diseases such as cancer, atherosclerosis, cataracts, and age-related macular degeneration as well as to premature aging. The free radical quenching constant of lycopene has been demonstrated to be more than twice that of β-carotene.        Lycopene is incorporated into lipoproteins. There it acts to decrease the oxidation of cholesterol, helping to prevent vascular damage.        Lycopene in the blood has been shown to be inversely proportional to the incidence of prostate tumors.        Research shows lycopene may provide protection against a broad range of epithelial cancers.        
Carotenoids are broadly used as dietary supplements due to their antioxidant potential, and lycopene has a strong presence in the nutraceuticals market.
Processes for preparing tomato concentrates have been reported. U.S. Pat. No. 3,172,770 relates to a process for preparing a tomato concentrate by means of crushing tomatoes and separating the juice into pulp and serum by centrifugation.
Processes for extraction of carotenoids have been reported. U.S. Pat. No. 5,837,311 to Zelkha et al. describes a process in which crushed, heated tomatoes are fractionated into serum and pulp containing at least 500 ppm lycopene; the lycopene is extracted from the pulp using a solvent. The solvents listed by patentees as satisfactory are hexane, ethyl acetate, and dichloromethane; however, neither dichloromethane nor hexane are environmentally friendly. U.S. Pat. No. 5,871,574 to Kawaragi et al. uses an enzymatic technique to macerate tomato pulp to facilitate easier downstream processing. Their downstream processing entails centrifuging to recover the liquid portion and then passing this liquid through a microfilter and collecting the retentate. This enables an appropriate microfractionation to optimize pigment size. The crude pigment may be further purified by agitation in 75% organic solvent such as methanol, ethanol, propanol, or acetone, and then recovering the sediment. The sediment is then dried to yield a tomato pigment. U.S. Pat. No. 5,773,075 to Todd describes high temperature countercurrent solvent extraction of Capsicum solids using edible solvents such as edible oils or fats or derivatives thereof. U.S. Pat. No. 5,897,866 to Bombardelli et al. describes a process to obtain lycopene wherein partially dehydrated whole fruits of Lycopersicum esculentum (tomato) are extracted with a solvent in the presence of phospholipids as surfactant and stabilizing agents and the extracts are concentrated or fractionated to an oil. The preferred solvents are n-hexane and methylene chloride, and the preferred phospholipid is soy lecithin. PCT Application No. WO 01/38443 A1 to Bortlik et al. describe a process for extraction of lycopene from tomatoes and tomato pomace using boiling ethanol. U.S. Pat. No. 6,818,239 to Kagan et al. describes a process for the extraction of carotenoids from a carotenoid source such as a biomass, which comprises treating the carotenoid source at an elevated temperature with a solvent mixture comprising water, a hydrophobic carotenoid solvent such as vegetable oil and a water soluble co-solvent such as ethanol so as to extract the carotenoid source into the hydrophobic solvent. U.S. Pat. No. 5,714,658 to Heidlas et al. describes extraction of carotenes from natural sources, by contacting the starting material with a solvent mixture composed of at least one acetic ester of C1-C4 alcohols and 1 to 25% by weight of an oil of biological origin at a temperature of at least 30° C. U.S. Pat. No. 5,789,647 to Heidlas et al. describes extraction of carotenoid dyes from pre-dried natural starting materials using compressed gases such as propane or butane and optionally an organic entraining agent such as acetone, ethyl acetate, or ethanol. U.S. Pat. No. 5,245,095 to Graves et al. describes a process of extraction of carotenoids from carrots wherein a carotenoid-precipitation agent including calcium chloride, calcium hydroxide, calcium lactate, or calcium gluconate is added to a liquid fraction obtained from a carotenoid-containing natural source to form a carotenoid-enriched solid precipitate. U.S. Pat. No. 5,830,738 to Thomas et al. describes a process for extracting carotenoids from pigmented plant material, which includes contacting shredded plant material with an enzyme.
Processes to extract carotenoids such as lycopene using supercritical CO2 have been described. See Ollanketo et al., European Food Research Technologies 212: 561-565, 2001, Rozzi et al., Journal of Agriculture and Food Chemistry 50:2638-2643, 2002, and U.S. Patent Applications 20030180435 and 20040131733.